1. Field of the Invention
This invention relates to the synchronous movement of an index film at a speed slow enough to visually ascertain its content in conjunction with a high speed data microfilm, and more particularly, to a direct mechanical drive responsive to data film movement.
2. Description of the Prior Art
A roll of microfilm or the like contains voluminous amounts of data with a single roll containing in excess of 100,000 pages of data which may be readily optically displayed by locating a particular page by high speed movement of the microfilm, termination of film movement and optical projection of that data. The data film itself travels so fast that it is impossible for the operator in moving the film to read any component of the data pages as they are flashed on the screen of the viewing element of the projection system during such movement. Conventionally, it is necessary for the operator to stop the data film near an expected point relative to the selected page or pages of data and ascertain whether, by hit or miss, he must then index the microfilm forward or rearward from that point and repeat the process in narrowing multiple steps as he nears a selected page.
Attempts have been made to provide on a separate film, index data and to synchronize movement of the index film at a much slower speed with that of the moving data film, so that the operator simply monitors the movement of the slow speed index film and stops the movement of the data film at the desired position.
To achieve such synchronism, optical marks have been placed in one or both films and a comparison made by optical comparing means of the position of the data film relative to the index film moving at the slower speed. However, the optical comparison means increases the cost of the microfilm viewer, complicates the system, and increases the size of the unit by the addition of the comparison means.